1. Field of the Invention
This invention concerns a cassette for an electrophoresis system including an essentially plate shaped body comprising wall means for supporting a gel plate.
This invention also concerns an electrophoresis system using such a cassette.
2. Description of the Background Art
Electrophoresis is a commonly used method for analysis, wherein charged molecules and particles migrate in a separation medium, usually a gel, which is subjected to an electrical field between two electrodes. Provided the electrical field is constant each molecule migrates with a constant speed which is determined by parameters such as field intensity and gel density but also by molecule parameters such as charge and size.
The separation medium is usually placed on a support and each side of the medium is contacted with an electrode buffer. The electrodes may be inserted in vessels containing the electrode buffers. The buffer solutions form both the electrolytic medium and a reservoir for ions to keep the pH and other parameters constant. After separation the molecules are detected and identified in different manners such as staining the gel or by optical means such as scanning by laser.
Gel electrophoresis is today routinely used for separating biomolecules such as proteins, peptides, nucleic acids etc. Often a lot of samples are handled e.g. in different types of screening or in clinical tests with samples from many patients. The electrophoretic conditions for different types of molecules are different and have to be adapted in each case. Thus, both the gel and the buffer solutions must be chosen for each type of sample.
The preparation of the electrophoresis process includes several rather laborious steps. A suitable gel is chosen and placed on a support. The gel is contacted with the buffer solutions. A common way is to have a gel slab in a cassette of glass or plastic in contact with the buffer solutions in buffer tanks. For each run the gel has to be placed on the support or the cassette be prepared. Then the buffer tanks are filled with buffer solutions and the samples are applied to the gel. To do away with the handling of buffer solutions in buffer tanks it has been suggested, in WO 87/04948, to incorporate the buffer substance in a gel material whereby the buffer is obtained in the form of a buffer strip. The buffer strips are much easier to handle, but still there remainder steps of adding all components together, which are time consuming and prevent automated handling. There is also a risk of mixing up samples with the many manual steps.
It is an aim of this invention to provide a solution to the above indicated problems and to provide a safe and effective means for use in an electrophoresis system.
This aim is obtained by providing a cassette and an electrophoresis system claimed in the claims. According to the invention a cassette for an electrophoresis system including an essentially plate shaped body is obtained. The plate shaped body comprises first wall means for supporting a gel plate and second wall means for supporting buffer strips, said wall means being connected to each other.
The cassette is characterized in that the second wall means are displaceable with respect to the first wall means between a first inactive position wherein the buffer strips are chemically and electrically separated from the gel plate and a second, active position where they are in electrical and chemical contact therewith.
With the cassette according to the invention it is possible to offer a xe2x80x9ctailor-madexe2x80x9d, tuned unit comprising buffer, gel and added samples, a unit which can be added directly to the electrophoresis system. For each cassette, buffer strips and a gel plate which are specifically adapted for a particular application may be provided.
The buffer solution included in the buffer strips may readily be carefully adapted to the electrophoresis procedure to be performed, and by having the buffer strips chemically and electrically isolated from the gel plate, it is assured that no chemical influences, such as dilution or migration of buffer solution, affect the gel plate because of contact with the gel plate. By having the buffer strips isolated from the gel plate in the inactive position and not allowing electrical and chemical contact therebetween until after displacing the second wall means and thereby the buffer strips into the second, active, position it is therefore assured that the properties of the buffer strips are not changed or deteriorated, which could otherwise be the case.
In this manner the user of the cassette knows that the rust from the electrophoresis will have a certain quality. This is especially important in analysis where a high degree of accuracy is necessary. For example, in searching for a suitable donor for transplantation, HLA (human leukocyte antigen) analysis is made, as these antigens are known to be the major target molecules for transplantation rejection. On the nucleic acid level, it is then important that the DNA sequence in a specific position is very clear. The resolution of the sequence in a DNA analysis is determined byte buffers and the gel parameters and running conditions.
Further, an important advantage with a further aspect of the invention is that the samples may be loaded on the gel in the cassette, which in that case may be sealed or covered and the unit can then be stored. Traditionally, the samples are applied to the gel in the electrophoresis apparatus. With this invention it is easier to handle samples in a safe manner. Samplers like blood for exhale, have to be handled in special rooms due to, among other things, the risk of infection. The samples is prepared e.g. by centrifuging etc. and in the end is applied on the gel. With this invention all sample preparation can be made at one place and the cassette with samples can be stored for later use without any risk for mixing-up, contamination or transmission of infection.
U.S. Pat. No. 5,582,702 concerns a cassette wherein the gel body is in permanent contact with the buffer bodies. Therefore, this cassette suffers from the above-mentioned disadvantages.
By the second wall means being displaceable by means of a linear movement it is possible to predetermine the contact pressure by dimensioning the cassette itself.
By the second wall means being displaceable by means of a pivoting movement simplicity is obtained in manufacture as well as in handling. The contact between the buffer strips and the gel plate is easily obtained.
By the buffer strips being separated from the gel plate by means of removable isolating elements in the inactive position it is possible to manufacturing particularly compact cassettes.
By the buffer strips and at least a part of the gel plate being protected by protective strips in the inactive position separation against the environment is assured.